As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as mobile devices.
Depending upon kinds of external devices in which secondary batteries are used, the secondary batteries may be configured to have a detachable type structure in which the secondary batteries can be easily inserted into and removed from the external devices or to have an embedded type structure in which the secondary batteries are embedded in the external devices. For example, it is possible for a user to insert or remove a battery into or from a device, such as a laptop computer. On the other hand, a device, such as a mobile phone, a MPEG audio layer-3 (mp3) player, a tablet PC or a smart pad, requires an embedded type battery pack due to the structure and capacity thereof.
Meanwhile, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or other physical external impact. That is, the safety of the lithium secondary battery is very low. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as the overcharge of the lithium secondary battery or the overcurrent in the lithium secondary battery, are connected to a battery cell.
Generally, an embedded type secondary battery pack uses a plate-shaped battery cell, which is suitable for electrical connection, and a PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, the nickel plates are connected to electrode terminals of the battery cell by welding or soldering, a printed circuit board (PCB) is attached to one side of a double-sided adhesive tape, a protective tape is attached to the other side of the double-sided adhesive tape, and electrode tabs of the PCB and the nickel plates are connected to each other by welding in a state in which the PCB is in tight contact with the battery cell. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is required for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell.
To this end, insulative tapes are attached to various members, including the PCM. In addition, a sealed portion of a battery case, in which the battery cell is mounted, is partially bent, and an insulative tape is attached to it or a barcode is printed on it. That is, the process is very complicated.
Since a plurality of insulative tapes or parts is required to achieve safe connection as described above, a battery pack assembly process is complicated, and manufacturing cost is increased.
Also, when external impact is applied to the battery pack, the PCM may be damaged or dimensional stability may be greatly lowered due to the use of the insulative tapes, which exhibit low mechanical strength.
Therefore, there is a high necessity for a technology that is capable of reducing the number of members mounted to a battery cell to simplify an assembly process, achieving stable coupling between members loaded in the battery cell and protecting a PCM.
Furthermore, there is also a high necessity for a battery pack that is capable of providing large capacity while having the same size in consideration of the development trend of a device, the weight and size of which are reduced.